This invention relates to a receiver circuit, in particular for receiving signals in which a portion of a transmitted signal is repeated after a known time interval.
The European DVB-T (Digital Video Broadcasting-Terrestrial) standard for digital terrestrial television (DTT) uses Coded Orthogonal Frequency Division Multiplexing (COFDM) of transmitted signals.
Received signals are sampled in a receiver, and accurate reception and demodulation of signals requires the sampling rate to be synchronized with the signal rate. For that purpose, DVB-T COFDM signals contain pilot signals which provide information allowing control of the sample rate. However, conventional techniques for extracting and using this information require considerable signal processing, with associated time delays.
It is an object of the present invention, in particular embodiments to provide a receiver which overcomes some of the disadvantages of the prior art.
This invention relates in a first aspect to a receiver which can conveniently extract information relating to the sample rate, as compared with the received signal rate, thereby advantageously allowing feedback control of the sample rate of the receiver.
According to a second aspect of the invention, there is provided a method of processing received signals, and controlling the sampling rate of a receiver.
In particular, according to the invention, there is provided a receiver circuit, comprising:
a sampler, for taking digital samples of a received signal at a sampling rate, said received signal including at least a first portion and a second portion which repeats the content of the first portion after a repeat interval;
at least one correlator for measuring:
a first correlation between the first portion of the signal, delayed relative to the second portion by a first delay equal to the repeat interval plus a difference interval, and the second portion of the signal; and
a second correlation between the first portion of the signal, delayed relative to the second portion by a second delay equal to the repeat interval minus a difference interval, and the second portion of he signal;
means for comparing the measured first and second correlations to produce a comparison output; and
means for controlling the sampling rate of the receiver on the basis of the comparison output in order to tend to equalize the first and second correlations.